Boride-based refractory materials

ABSTRACT

The invention provides a novel highly refractory sintered body based on a tal diboride such as TiB 2  or Mo 2  B 5  and W 2  B 5  containing a binder ingredient. The high-temperature performance of the sintered body is further improved by including an auxiliary additive ingredient selected from several carbides, nitrides, silicides and oxides such as WC, TiC, TaN, TiN, MoSi 2 , TiO 2 , Al 2  O 3 , B 2  O 3  and the like in a limited amount.

BACKGROUND OF THE INVENTION

The present invention relates to a boride-based refractory material or,more particularly, to a boride-based refractory material havingremarkably improved mechanical strengths and hardness at hightemperatures as well as high heat resistance based on a metal diborideof the MB₂ type or an equivalent boride such as M₂ B₅ type boride as thebase component.

Among various classes of highly refractory materials, metaldiboride-based ones belong to one of the most promising classes owing totheir high melting points and high hardness as well as sufficiently highmechanical strengths at high temperatures in general so that theirapplication to cutting tools and building materials for internalcombustion engines and rockets and the like is now under rapiddevelopment. On the contrary to the above mentioned excellent propertiesof the metal diboride-based refractory materials, they are ratherdefective of the brittleness and low bending strength, especially, whenthe refractory material is composed essentially of a metal diboride ofthe MB₂ type or a metal boride of the M₂ B₅ type which may becrystallographically equivalent to the MB₂ type diboride at elevatedtemperatures.

Extensive investigations have hitherto been undertaken to develop ametal diboride-based refractory material fully exhibiting the excellentproperties inherent to the metal diborides and still free from the abovementioned defects of brittleness or low bending strength of the priorart materials. The investigations have been directed to the improvementof the material by the addition of a suitable binder component to ametal diboride and there have been proposed several kinds of binderswhich may be an alloy of nickel and phosphorus or a boride of nickel,iron, cobalt, manganese or titanium. There has further been disclosedthat a metal boride of the M₂ B₅ type such as W₂ B₅ and Mo₂ B₅, whichhas the same crystallographic structure at high temperatures as themetal diborides of the MB₂ type, is more advantageous in a sinteredrefractory material in respect of the mechanical strengths at hightemperatures (see, for example, copending U.S. applications Ser. Nos.89,487, 973,957 and 127,434 now U.S. Pat. Nos. 4,259,119; 4,246,027; and4,292,081, respectively).

It is of course desirable to obtain a metal diboride-based refractorymaterial having still higher strengths than those obtained in the abovedescribed impoved formulations and the inventors have continued theirefforts to discover more preferable formulations for a high-strengthrefractory material on the base of a metal diboride.

SUMMARY OF THE INVENTION

As a result of the above mentioned continued efforts undertaken by theinventors, it has been unexpectedly discovered that the mechanicalstrengths of the metal diboride-based refractory materials can furtherbe improved by the addition of a suitable amount of an additiveingredient which may be a carbide, oxide, silicide or nitride ofspecified elements as defined hereinafter.

The metal diboride-based refractory material of the invention comprisesthe components of

(a) at least one metal boride selected from the group consisting of theMB₂ type diborides of titanium, vanadium, niobium, tantalum, chromium,molybdenum, manganese, zirconium, hafnium and aluminum and M₂ B₅ typeborides of molybdenum and tungsten,

(b) from 0.01 to 50% by weight of at least one binder ingredientselected from the group consisting of the borides of nickel, iron,cobalt, manganese and titanium other than the MB₂ type diborides andalloys of nickel and phosphorus, and

(c) from 0.1 to 50% by weight of at least one additive ingredientselected from the group consisting of

(c-1) carbides expressed by the formulas TiC, ZrC, HfC, VC, NbC, TaC,Ta₂ C, Mo₂ C, MoC, Cr₃ C₂, B₄ C, W₂ C, WC and SiC;

(c-2) silicides expressed by the formulas MoSi₂, WSi₂, CrSi, CrSi₂, Cr₃Si, TaSi₂, NbSi₂, VSi₂, ZrSi₂ and TiSi₂ ;

(c-3) nitrides expressed by the formulas TiN, TaN, Ta₂ N, ZrN, HfN, VN,V₃ N, NbN, Nb₂ N, CrN, Cr₂ N, Mo₂ N and MoN; and

(c-4) oxides expressed by the formulas Al₂ O₃, B₂ O₃, SiO₂, Cr₂ O₃, TaO,VO, NbO, BeO, TiO, TiO₂, Ti₂ O₃, ZrO₂.SiO₂, Al₂ O₃.TiO₂, MgO.Al₂ O₃,ThO₂.ZrO₂, 3Al₂ O₃.SiO₂ and (Mg,Fe) (Al,Cr)₂ O₄, the balance beingsubstantially the metal boride as the component (a).

Further improvement in the mechanical strengths of the metaldiboride-based refractory materials of the above defined formulation isobtained when the composition additionally contains (d) up to 40% byweight, based on the total amount of the sintered material, of a MB typeboride of a metal selected from the group consisting of tantalum,niobium, tungsten, zirconium, hafnium, molybdenum and vanadium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As is described above, the inventive metal diboride-based refractorymaterial is basically composed of the base boride as the component (a),the binder ingredient as the component (b) and the auxiliary additiveingredient as the component (c) in the above specified proportion,optionally, with addition of the MB type boride as the component (d)partially substituting for the base component (a). The addition of thiscomponent (d) is preferable when further increased strength of therefractory material is desired and such an additional improvement isobtained by adding 0.1% by weight or more of the component (d) while anamount in excess of 40% by weight is undesirable due to the increaseddifficulty in sintering the composition into refractory bodies.

The amount of this base component constitutes the balance of the othercomponents but it is preferable that the amount of the MB₂ and/or M₂ B₅type boride or borides is at least 30% by weight of the totalformulation. Among the above named 10 kinds of the metal diborides,titanium diboride is preferred solely for the reason of lessexpensiveness than the other diborides which also can give equallyexcellent refractory bodies.

The base component, i.e. the component (a) with optional admixture ofthe component (d), is used as a fine powder having a particle sizedistribution of 5 μm or smaller in the average particle diameter.

The binder ingredient as the component (b) is essential to facilitatesintering of the composition so that it should be used in an amount ofat least 0.01% by weight based on the total amount of the composition tobe sintered while an amount in excess of 50% by weight of the binderingredient is undesirable due to the decreased heat resistance of theresultant sintered refractory bodies. The amount of this binderingredient is preferably in the range from 0.1 to 20% by weight when therefractory body is prepared by the techniques of so-called hot pressingand in the range from 15 to 40% by weight when the refractory body isprepared by the method of sintering a green body shaped by compressionmolding in cold or by the method of so-called infiltration.

The binder ingredient as the component (b) is, as is described above,selected from the borides of nickel, cobalt, iron, manganese andtitanium as well as alloys of nickel and phosphorus. Suitable borides ofnickel are exemplified by NiB, Ni₄ B₃, Ni₂ B and Ni₃ B, cobalt boridesare exemplified by CoB, Co₂ B and Co₃ B, iron borides are exemplified byFeB and Fe₂ B, manganese borides are exemplified by MnB, Mn₃ B₄, Mn₂ Band Mn₄ B, and titanium borides are exemplified by TiB, Ti₂ B and Ti₂B₅. These borides may be used either singly or as a mixture of two kindsor more. Particularly suitable metal borides among them are NiB, Ni₄ B₃,CoB, FeB, TiB and MnB. The alloy of nickel and phosphorus used as thecomponent (b) is obtained by adding from 3 to 25% by weight ofphosphorus to nickel. It is of course optional that the binderingredient as the component (b) is a combination of one or more of themetal borides as defined above and the nickel-phosphorus alloy. Amongthe above named borides suitable as the binder ingredient, MnB, TiB,NiB, Ni₄ B, CoB and FeB are more preferable.

It should be noted that the above defined binder ingredient is notnecessarily added in the form described above as such but may be amixture of the components from which the above mentioned borides or thealloys can be formed during the sintering procedure. For example, ametal such as nickel, cobalt, iron, manganese and titanium may be addedas combined with elementary boron so as that the desired metal boride isformed by the reaction between the metal and the boron during sintering.

The auxiliary additive ingredient as the component (c), which isformulated in an amount from 0.1 to 50% by weight or, preferably, from 1to 30% by weight, is selected from the above named carbides, silicides,nitrides and oxides. Among the above named ones, WC, TiC, TaC, NbC, VCand ZrO₂ are more preferable and the nitrides such as TiN, ZrN, TaN andVN are effective to improve the impact strength of the sinteredrefractory body. MoSi₂, ZrSi₂, B₂ O₃ and Al₂ O₃ are less preferable.These auxiliary additive ingredients should have a particle diameter notto exceed 5 μm. These ingredients may be added either alone or as acombination of two kinds or more.

The sintered refractory body of the invention is manufactured asfollows. The individual components are taken in calculated amounts anduniformly blended to give a powdery composition. A mold made of, forexample, graphite is filled with the powder composition and sintering ofthe composition is carried out by heating the composition in the mold ata temperature of 1000° C. or higher or, preferably, from 1700° to 1800°C. under a pressure of at least 50 kg/cm² or preferably, at least 200kg/cm² in vacuum or in an inert or reducing atmosphere of argon orhydrogen for about 10 minutes or longer. Instead of the above describedso-called hot-pressing, it is of course possible that a green body isfirst shaped by compression molding a room temperature with the powdercomposition and the green body of the desired form is then subjected tosintering under atmospheric pressure otherwise with the above describedconditions into a sintered body.

Further alternatively, the techniques of the so-called infiltration areapplicable in this case. That is, the metal diboride and/or the M₂ B₅type boride with optional admixture of MB type borides are blended withthe auxiliary additive ingredient of the carbides, nitrides, silicidesor oxides and the powder blend is first shaped and sintered without thebinder ingredient followed by dipping of the thus sintered body in amelt of the binder ingredient so as that the molten binder is soaked inthe sintered body resulting in the desired sintered body.

In any way, the sintered refractory body of the invention always has arelative density of approximately 100% and is excellent in themechanical strengths, hardness and heat resistance and advantageouslyutilized for the manufacture of cutting tools or as a structuralmaterial of internal combustion engines, rockets and the like.

Following are the examples to illustrate the present invention infurther detail.

EXAMPLE (EXPERIMENTS NO. 1 to NO. 43)

One or two kinds of the base borides selected from the MB₂ type and M₂B₅ type borides always including titanium diboride TiB₂ were admixedwith a binder boride, i.e. CoB, NiB, FeB or TiB, and one to three kindsof the auxiliary additive ingredients selected from the carbides,nitrides, silicides and oxides. The kinds of the admixed ingredients ineach of the experiments excepting titanium diboride are shown in theaccompanying table with the amount of each of the ingredients indicatedin brackets in % by weight, the balance being the amount of titaniumdiboride. In Experiment No. 22, tantalum boride TaB was used topartially substitute for the MB₂ or M₂ B₅ type borides.

A graphite mold was filled with the thus well blended powder mixturewhich was sintered under compression with a pressure of 200 kg/cm² for30 minutes. The heating temperature was 1700° C. in all of theExperiments excepting No. 2 in which the sintering was carried out at1800° C. The atmosphere of sintering was evacuated to vacuum in all ofthe Experiments excepting No. 21 in which the sintering was carried outin an atmosphere of argon.

All of the sintered bodies obtained in this manner had a relativedensity of almost 100% of the theoretical value. The sintered bodieswere subjected to the measurements of the bending strength and theVickers hardness both at room temperature and at 1000° C. to give theresults shown in the table.

                                      TABLE                                       __________________________________________________________________________                                Vickers hardness,                                                       Bending                                                                             kg/mm.sup.2                                       Exp.                                                                              Component         strength,                                                                           at room                                                                             at                                          No. a* (%)                                                                              b (%) c (%) kg/mm.sup.2                                                                         temp. 1000° C.                             __________________________________________________________________________    (Part I)                                                                      1   Mo.sub.2 B.sub.5 (3)                                                                CoB (1)                                                                             Mo.sub.2 C (3)                                                                      220   3000  2000                                        2   W.sub.2 B.sub.5 (5)                                                                 CoB (1)                                                                             WC (5)                                                                              200   2800  --                                          3   TaB.sub.2 (5)                                                                       CoB (1)                                                                             WC (5)                                                                              186   --    --                                          4   Mo.sub.2 B.sub.5 (3)                                                                CoB (1)                                                                             TiC (5)                                                                             226   2900  2000                                        5   TaB.sub.2 (5)                                                                       CoB (1)                                                                             TiC (1.7)                                                                           230   3000  2100                                        6   TaB.sub.2 (5)                                                                       CoB (1)                                                                             TiC (3)                                                                             230   --    --                                          7   TaB.sub.2 (5)                                                                       CoB (1)                                                                             Mo.sub.2 C (3)                                                                      210   2900  2000                                        8   TaB.sub.2 (5)                                                                       CoB (1)                                                                             TaN (5)                                                                             198   --    --                                          9   TaB.sub.2 (5)                                                                       CoB (1)                                                                             TaN (10)                                                                            228   2910  2000                                        10  TaB.sub.2 (5)                                                                       CoB (1)                                                                             TaN (20)                                                                            182   --    --                                          11  TaB.sub.2 (5)                                                                       CoB (1)                                                                             TaN (30)                                                                            178   --    --                                          12  TaB.sub.2 (5)                                                                       CoB (1)                                                                             TiN (6)                                                                             188   --    --                                          13  TaB.sub.2 (5)                                                                       CoB (1)                                                                             TiN (2)                                                                             185   --    --                                          14  TaB.sub.2 (5)                                                                       CoB (1)                                                                             TiC (3)                                                                             200   --    --                                                          TaN (10)                                                      (Part II)                                                                     15  TaB.sub.2 (5)                                                                       CoB (1)                                                                             TiC (3)                                                                             204   --    --                                                          TaN (20)                                                      16  TaB.sub.2 (5)                                                                       CoB (1)                                                                             TiC (1.7)                                                                           250   3000  2100                                                        TaN (5)                                                       17  TaB.sub.2 (5)                                                                       CoB (1)                                                                             TiC (1.7)                                                                           250   --    --                                                          TaN (10)                                                      18  TaB.sub.2 (5)                                                                       CoB (1)                                                                             TiC (1.7)                                                                           196   --    --                                                          TaN (20)                                                      19  TaB.sub.2 (5)                                                                       CoB (1)                                                                             MoSi.sub.2 (5)                                                                      194   --    --                                          20  Mo.sub.2 B.sub.5 (3)                                                                CoB (1)                                                                             MoSi.sub.2 (3)                                                                      172   --    --                                          21    --  NiB (1)                                                                             MoSi.sub.2 (5)                                                                      164   --    --                                          22  TaB** (5)                                                                           TiB (1)                                                                             TiC (3)                                                                             200   2900  2000                                                        TaN (5)                                                                       MoSi.sub.2 (3)                                                23  TaB.sub.2 (5)                                                                       CoB (1)                                                                             TiO.sub.2 (5)                                                                       190   3000  2000                                        24  VB.sub.2 (5)                                                                        FeB (1)                                                                             Ti.sub.2 O.sub.3 (5)                                                                180   --    --                                          25  CrB.sub.2 (5)                                                                       CoB (1)                                                                             TiO (5)                                                                             174   --    --                                          26  TaB.sub.2 (5)                                                                       CoB (1)                                                                             TiC (1.7)                                                                           230   3200  2100                                                        TaN (5)                                                                       TiO.sub.2 (5)                                                 27  TaB.sub.2 (5)                                                                       CoB (1)                                                                             B.sub.2 O.sub.3 (5)                                                                 180   --    --                                          28  TaB.sub.2 (5)                                                                       CoB (1)                                                                             WC (1)                                                                              160   --    --                                          29  TaB.sub.2 (5)                                                                       CoB (1)                                                                             WC (2.5)                                                                            144   --    --                                          (Part III)                                                                    30  TaB.sub.2 (1)                                                                       CoB (1)                                                                             WC (10)                                                                             160   3100  2200                                        31    --  CoB (1)                                                                             WC (2.5)                                                                            200   2800  2000                                        32    --  CoB (1)                                                                             WC (5)                                                                              200   --    --                                          33    --  CoB (1)                                                                             WC (10)                                                                             200   --    --                                          34    --  CoB (1)                                                                             TiC (10)                                                                            140   2800  2000                                        35    --  CoB (1)                                                                             TiC (20)                                                                            140   --    --                                          36  Mo.sub.2 B.sub.5 (3)                                                                CoB (1)                                                                             Mo.sub.2 C (3)                                                                      210   2910  2000                                        37  TaB.sub.2 (5)                                                                       CoB (3)                                                                             B.sub.4 C (5)                                                                       150   2800  --                                          38  TaB.sub.2 (5)                                                                       CoB (1)                                                                             TaC (5)                                                                             200   3000  2200                                        39  TaB.sub.2 (5)                                                                       CoB (1)                                                                             NbC (5)                                                                             200   3000  2200                                        40  TaB.sub.2 (5)                                                                       CoB (1)                                                                             VC (5)                                                                              200   3000  2200                                        41  TaB.sub.2 (5)                                                                       CoB (1)                                                                             VN (5)                                                                              180   2800  --                                          42  TaB.sub.2 (5)                                                                       CoB (1)                                                                             ZrO.sub.2 (2)                                                                       230   3000  2100                                        43  TaB.sub.2 (5)                                                                       CoB (1)                                                                             ZrO.sub.2 (2)                                                                       230   3100  2100                                                        WC (2)                                                                        TaN (5)                                                       __________________________________________________________________________     *Other than titanium diboride.                                                **TaB was used in place of part of the component (a).                    

What is claimed:
 1. A refractory sintered body composed essentiallyof(a) at least 30% by weight of at least one metal boride selected fromthe group consisting of MB₂ type diborides of titanium, vanadium,niobium, tantalum, chromium, molybdenum, manganese, zirconium, hafnium,and aluminum and M₂ B₅ type borides of molybdenum and tungsten, (b) from0.01 to 50% by weight of at least one binder ingredient selected fromthe group consisting of the borides of nickel, iron, cobalt, manganeseand titanium other than the MB₂ type diborides and alloys of nickel andphosphorus, and (c) from 0.1 to 50% by weight of at least one additiveingredient selected from the group consisting of WC, TiC, TaC, NbC, VC,ZrO₂, TiN, ZrN, TaN, and VN, the balance being substantially the metalboride of the component (a), or (d) the metal boride of the component(a) and up to 40% by weight, based on the sintered body, of at least oneMB type boride of a metal selected from the group consisting oftantalum, niobium, tungsten, zirconium, hafnium, molybdenum, andvanadium.
 2. The refractory sintered body as claimed in claim 1 whereinthe binder ingredient as the component (b) is selected from the groupconsisting of MnB, TiB, NiB, Ni₄ B, CoB and FeB.
 3. The refractorysintered body as claimed in claim 1 in which the balance issubstantially the metal boride of the component (a).
 4. The refractorysintered body as claimed in claim 1 in which the balance issubstantially the metal borides of the component (d).
 5. The refractorysintered body of claim 1 or claim 4 which contains MB₂ type titaniumdiboride.
 6. The refractory sintered body of claim 1 having a bendingstrength greater than 200 Kg/mm², and a Vickers hardness of at least2000 at 1000° C.